Refrigeration systems are used in many applications for heating and cooling a controlled environment, including a cargo box on a transport truck, train, ship or plane. The refrigeration system has many components including a condenser, an evaporator, and a compressor. The compressor typically includes a plurality of cylinder banks, where at least one of the cylinder banks has an unloader for loading and unloading the cylinder bank. Before transporting cargo, it is desirable to determine whether the refrigeration system is in an operational condition.
There have been some attempts to use a pretrip device to determine the operational condition of the refrigeration system prior to transportation. One such device to Hanson et al., U.S. Pat. No. 5,172,561, includes a pretrip device which determines the operational condition of the refrigeration system as a function of temperature change. When the box is humid, the refrigeration system will remove moisture from the air prior to changing the temperature. As a result, this device has a propensity for false alarms. Further, this device does not have the capability to isolate the particular problem within the refrigeration system.
When an alarm is signaled, the refrigeration system must be taken out of service and be inspected for problems, which takes time and costs money. When the alarm is false, it takes longer to service because there are no identifiable problems.
Further, the pretrip device of Hanson et al. does not have the capability to identify a particular problem with or within a compressor. As a result, the entire refrigeration system must be tested by a technician in order to isolate and repair a problem within a compressor. Due to the mechanical complexity of a compressor including many components, troubleshooting a compressor results in a significant loss of time and money.